This invention relates to magnetic recording media, such as thin film magnetic recording disks, and to a method of manufacturing the media. The invention has particular applicability to high areal density magnetic recording media exhibiting low noise, and high coercivity.
The increasing demands for higher areal recording density impose increasingly greater demands on thin film magnetic recording media in terms of remanent coercivity (Hr), magnetic remanance (Mr), coercivity squareness (S*), medium noise, i.e., signal-to-medium noise ratio (SMNR), and narrow track recording performance. It is extremely difficult to produce a magnetic recording medium satisfying such demanding requirements.
The linear recording density can be increased by increasing the Hr of the magnetic recording medium, and by decreasing the medium noise, as by maintaining very fine magnetically non-coupled grains. Medium noise in thin films is a dominant factor restricting increased recording density of high-density magnetic hard disk drives, and is attributed primarily to inhomogeneous grain size and intergranular exchange coupling. Accordingly, in order to increase linear density, medium noise must be minimized by suitable microstructure control.
A conventional longitudinal recording disk medium is depicted in FIG. 1. It typically comprises a non-magnetic substrate 10 having sequentially deposited on each side thereof an underlayer 11, 11xe2x80x2, such as chromium (Cr) or Cr-alloy, a magnetic layer 12, 12xe2x80x2, typically comprising a cobalt (Co)-base alloy, and a protective overcoat 13, 13xe2x80x2, typically containing carbon. Conventional practices also comprise bonding a lubricant topcoat (not shown) to the protective overcoat. Underlayer 11, 11xe2x80x2, magnetic layer 12, 12xe2x80x2, and protective overcoat 13, 13xe2x80x2, are typically deposited by sputtering techniques. The Co-base alloy magnetic layer deposited by conventional techniques normally comprises polycrystallites epitaxially grown on the polycrystal Cr or Cr-alloy underlayer. A conventional perpendicular recording disk medium is similar to the longitudinal recording medium depicted in FIG. 1, but does not comprise Cr-containing underlayers.
Conventional methods for manufacturing longitudinal magnetic recording medium with a glass, glass-ceramic, Al or Alxe2x80x94NiP substrate comprise applying a seedlayer between the substrate and underlayer. A conventional seedlayer seeds the nucleation of a particular crystallographic texture of the underlayer. Typically, a seedlayer is the first deposited layer on the non-magnetic substrate. The role of this layer is to texture (alignment) the crystallographic orientation of the subsequent Cr-containing underlayer.
Furthermore, there exists a texture relationship between the underlayer and the magnetic layer. Therefore, the influence of the seed layer in terms of a texture relationship permeates even into the magnetic layer.
Conventional Cr-alloy underlayers comprise chromium (Cr), vanadium (V), titanium (Ti), tungsten (W) or molybdenum (Mo). Conventional magnetic layers are CoCrTa, CoCrPtB, CoCrPt, CoCrPtTaNb and CoNiCr.
A conventional longitudinal recording disk medium is prepared by depositing multiple layers of metal films to make a composite film. In sequential order, the multiple layer typically comprise a non-magnetic substrate, one or more underlayers, a magnetic layer, and a protective carbon layer. Generally, a polycrystalline epitaxially grown cobalt-chromium (CoCr) alloy magnetic layer is deposited on a chromium or chromium-alloy underlayer.
The seedlayer, underlayer, and magnetic layer are conventionally sequentially sputter deposited on the substrate in an inert gas atmosphere, such as an atmosphere of argon. A conventional carbon overcoat is typically deposited in argon with nitrogen, hydrogen or ethylene. Conventional lubricant topcoats are typically about 20 xc3x85 thick.
It is recognized that the magnetic properties, such as Hr, Mr, So and SMNR, which are critical to the performance of a magnetic alloy film, depend primarily upon the microstructure of the magnetic layer which, in turn, is influenced by one or more underlying layers on which it is deposited. It is also recognized that underlayers having a fine grain structure are highly desirable, particular for growing fine grains of hexagonal close packed (HCP) CoCr deposited thereon to form an intermediate layer. The HCP layer is thin and is used to absorb the interfacial strain occurring from the transition from a cubic crystal structure of the underlayer to a HCP structure of the magnetic layer.
In co-pending U.S. patent application Ser. No. 09/152,326 filed on Sep. 14, 1998, a magnetic recording medium is disclosed comprising a surface oxidized NiAl seedlayer, and sequentially deposited thereon a Cr-containing underlayer, a CoCrTa intermediate layer and a CoCrPtTa magnetic layer.
Adding various elements, including oxygen, to one or more underlayers has been shown to increase the coercive force in recording media. U.S. Pat. No. 5,523,173 discloses that a higher SMNR can be obtained if boron is added to an magnetic layer consisting of a CoPtCr alloy with a 1120 crystallographic orientation deposited on an underlayer with 100 orientation. U.S. Pat. No. 5,316,631 to Ando et al., discloses the incorporation of oxygen into a Cr underlayer. The Cr underlayer contains 4 to 50 atomic percent oxygen. Oxygen may also be added to a CoCr underlayer in an amount of 15 to 30 atomic percent.
In order to squeeze as much digital information as possible on a recording disc medium there will be a continuing need for improved areal density magnetic recording media exhibiting high coercivity and high SMNR.
The invention provides a magnetic recording medium for high areal recording density exhibiting low noise, high coercivity. One way of achieving this goal is to produce a magnetic film with substantial directional magnetic isotropy.
Another aspect of this invention is a method of manufacturing a magnetic recording medium which exhibits excellent overwrite properties, little or no modulation of magnetic properties, relatively high SMNR and high areal recording densities.
An embodiment of this invention is a magnetic recording medium, comprising: a substrate; a seedlayer disposed on the substrate, wherein the seedlayer comprises a Crxe2x80x94X containing material; and a magnetic layer, wherein a solid solubility of the X is at least 3 atomic percent in Cr. Preferably, a heat of oxide formation of the X is less than that of Cr and a lattice tuning capability of the X is at least 2% that of Cr. Typically, X is selected from the group consisting of aluminum, calcium, titanium, vanadium, manganese, iron, cobalt, nickel, zinc, or a mixture thereof. The magnetic recording medium could further comprise an underlayer comprising a Cr-containing material, for example, a CoCr underlayer to form a first magnetic recording medium. The first magnetic recording medium could exhibit a stronger CoCr (11.0) peak by X-ray crystallography than that of a second magnetic recording medium that is similar to the first magnetic recording medium except that the seedlayer of the second magnetic recording medium contains substantially pure Cr with no Crxe2x80x94X containing material. For example, the seedlayer of the first magnetic recording medium could comprise Cr-10W and the CoCr underlayer could comprise Co-37Cr.
In another embodiment, the seedlayer could have a Crxe2x80x94X (110) interplanar spacing that is roughly equivalent to a (0002) interplanar spacing of a HCP alloy of a CoCr underlayer or a magnetic layer. In yet another embodiment of this invention, a portion of the seedlayer is oxidized.
One embodiment of this invention is a method of manufacturing a magnetic recording medium, comprising: depositing a seedlayer comprising a Crxe2x80x94X containing material on a substrate; and depositing a magnetic layer on the seedlayer, wherein a solid solubility of the X is at least 3 atomic percent in Cr.
Another embodiment of this invention is a magnetic recording medium comprising: means for low noise recording and a magnetic layer.
A xe2x80x9cmeans for low noise recordingxe2x80x9d comprises a layer comprising a Crxe2x80x94X containing material, wherein a solid solubility of said X is at least 3 atomic percent in Cr, a heat of oxide formation (xe2x88x92xcex1Hf) of said X is greater than 200 kcal/(gmol) or a lattice tuning capability of said X is at least 2% that of Cr. Preferably, the means for low noise recording is a seedlayer comprising a Crxe2x80x94X material, a portion of which is oxidized.
As will be realized, this invention is capable of other and different embodiments, and its details are capable of modifications in various obvious respects, all without departing from this invention. Accordingly, the drawings and description are to be regarded as illustrative in nature and not as restrictive.